PP has excellent mechanical properties. Its yield strength, tensile strength, compressive strength, hardness, and elastic modulus are higher than HDPE. However, at room temperature and low temperature, due to its high molecular structure regularity, the impact strength is relatively high. Poor; PP has outstanding bending fatigue strength, good heat resistance, and good friction resistance, but brittle cracking occurs at temperatures below -35 ° C, and cold resistance is not as good as polyethylene.
PP has good chemical stability. Except that it can be attacked by concentrated sulfuric acid and concentrated nitric acid, it is relatively stable against various other chemical reagents, but low molecular weight aliphatic hydrocarbons, aromatic hydrocarbons, and captured hydrocarbons can soften and swell polypropylene. ; PP has excellent high frequency insulation performance. Because it hardly absorbs water, the insulation performance is not affected by humidity. It has a high dielectric constant and can be used to make heated electrical insulation products. Its breakdown voltage is also very high. High, suitable for use as electrical accessories.
There are many molding methods for PP, such as injection molding, extrusion, blow molding, vacuum thermoforming, coating, rotary molding, welding, machining, electroplating and foaming, etc., and spraying on metal surfaces. When PP is in contact with the metal wall for a long time, it will decompose and carbonize, so care must be taken not to keep the material in the barrel for a long time during processing. During injection molding, in order to facilitate plasticization, it is best to lengthen the diverter shuttle of the injection molding machine. If you want to shorten the injection cycle, you can also increase the injection temperature appropriately, but it is limited to not causing serious degradation.
It is very important to choose an appropriate mold temperature during injection molding, because polypropylene molecules are prone to orientation, and after the molecular orientation, strain will occur and reduce the impact strength. Orientation phenomenon is most likely to occur during low temperature and high pressure injection, so the temperature cannot be too low (mold The temperature should be about 80 ℃, not lower than 50 ℃), or the surface gloss of the molded product is poor, or defects such as welding marks are generated. Of course, the mold temperature should not be too high, and the mold temperature will cause the product to warp. . PP's secondary processing performance is very good, its printing performance is better than polyethylene, products can be stamped, printed, plied, etc., electroplating is used for decorative parts of instruments, meters, electronics, etc.